Friction material and its manufacturing method

ABSTRACT

A friction material has a resin amount distribution that is the largest at a portion near a non-friction surface, that becomes lower toward an inside and that is the lowest at a portion near a friction surface. For example, such friction material is manufacture as follows. First, two friction materials are overlapped while the friction surfaces faced with each other. Then, the friction materials are dried at a room temperature. At this time, the resin has such a characteristic as to move while dragged by a solvent that dries from the non-friction surface located outside. Using such characteristic, the resin amount at the portion near the friction surface is lessened. Then, a temperature at the friction surface is made low and a temperature at the non-friction surface is made high in a drying step of the friction material. Thereby, the resin amount at the portion near the friction surface is lessened.

RELATED APPLICATION

This application is a divisional application of U.S. patent applicationSer. No. 12/318,184 filed on Dec. 23, 2008, which is a divisionalapplication of U.S. patent application Ser. No. 11/393,950 filed on Mar.31, 2006 now U.S. Pat. No. 7,488,440, issued Feb. 10, 2009, which is adivisional application of U.S. patent application Ser. No. 10/730,249filed on Dec. 9, 2003 now U.S. Pat. No. 7,051,858, issued May 30, 2006,which is hereby incorporated by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a friction material for a friction clutchdevice that has a single friction plate or a plurality of frictionplates for use in an automatic transmission of an automobile, atransmission of a motorcycle or the like, and to its manufacturingmethod.

2. Description of the Related Art

A wet friction clutch such as a multiplate clutch has one or a pluralityof wet friction plates that are used in a lubricant. There are wetfriction plates that are made of a sintered alloy, a carbon or a cork.Still, a paper wet friction plate is called as “a paper frictionmaterial” and is commonly used.

In manufacturing the paper wet friction material, a paper body is madeof a substrate fiber such as a pulp or an aramid fiber and a filler suchas a friction adjuster or a base filler. Next, the paper body isimpregnated with a resin binder made of a thermosetting resin. Then, thepaper body is heated to cure or harden the resin binder, therebyresulting in the paper wet friction material. Such paper wet frictionmaterial is advantageous because it is lightweight and cheap. Moreover,the paper wet friction material is made of a porous material andrelatively rich in elasticity with resultant high oil absorbency.Furthermore, the paper wet friction material is excellent in heatresistance, abrasion resistance and the like.

A resin existing near a friction surface of the friction material is oneof factors that determine the heat resistance (particularly a heat spotresistance) of the friction material. If an amount of the resin near thefriction surface is large, the friction material becomes hard and theheat resistance is lowered. Thus, it is thought that it is desirable forthe resin amount to be small.

However, if the total resin amount in the friction material is reducedso as to decrease the resin amount near the friction surface, it isimpossible to maintain strength required for the friction material.Therefore, a minimum amount of resin is mixed into the friction materialso as to balance the heat resistance and the strength.

Still, it is indispensable to remove the resin at the friction surfacein order to achieve an ultrahigh heat resistance required for thefriction material in these years. As a means to solve such problem, apost-treatment process such as a surface polishing or a high heat resindegradation (heat shearing) is added to improve the heat resistance.

However, if such post-treatment process is added, the costs increase.Moreover, there take place adverse effects in case of the post-treatmentprocess. That is, if the surface polishing is adopted, the friction faceof the friction material becomes rough or fuzzy so as to increase a dragtorque. On other hand, if the heat shearing is adopted, even an insideof the friction material reaches a high temperature so as to causedeterioration of strength or the like. Thus, it is very hard at presentto attain goals recently required for the friction material such as thelow costs and the ultrahigh heat resistance.

BRIEF SUMMARY OF THE INVENTION

An object of the present invention is to provide a friction material atlow costs that has an ultrahigh heat resistance without deterioration ofstrength and to provide a manufacturing method of such frictionmaterial.

According to a first aspect of the invention, there is provided afriction material comprising: a friction surface; a non-friction surfacelocated opposite to the friction surface; and a resin contained in thefriction material. A distribution of an amount of the resin in athickness direction from a side of the friction surface to a side of thenon-friction surface of the friction material is made lower at a portionnear the friction surface than a portion having a highest amount of theresin in the thickness direction.

Therefore, the resin amount at the portion near the friction surfacebecomes lower than that of an inside of the friction material or theportion near the non-friction surface. Consequently, the frictionmaterial is improved very much in a heat resistance and a heat spotresistance, thereby becoming ultrahigh heart resistant. Moreover, aresin amount distribution in the thickness direction of the frictionmaterial is determined by a drying step of the friction material.Therefore, a post-treatment process is unnecessary. Consequently, thefriction material can be ultrahigh heat resistant at low costs withoutdeterioration of strength.

The amount of the resin of the friction material may be made about 5% ormore lower at the side of the friction surface than at the side of thenon-friction surface.

In this case, the resin amount becomes lower at the portion near thefriction surface than at the portion near the non-friction surface.

The amount of the resin of the friction material may be made about 5% ormore lower at the side of the friction surface than at an inside of thefriction material.

In this case, the resin amount becomes lower at the portion near thefriction surface than at the inside of the friction surface.

The distribution of the amount of the resin of the friction material maychange in a continuous manner.

In this case, since the resin amount distribution changes continuously,no mechanical stress is concentrated on a specific part.

The distribution of the amount of the resin of the friction material maychange in a discontinuous manner.

In this case, the resin amount distribution in the thickness directioncan be determined by an overlapping. Consequently, the friction materialis improved very much in the heat resistance and the heat spotresistance at desired low costs.

The distribution of the amount of the resin of the friction material maybe formed by impregnation of the resin.

In this case, if a temperature at the friction surface is decreased anda temperature at the non-friction surface is increased in a drying stepafter the resin is impregnated, the resin in the friction material hassuch a characteristic as to move from a low temperature part to a hightemperature part while led by a solvent that moves toward the hightemperature part so as to be dried. Consequently, the resin amountdistribution in the thickness direction becomes the highest at theportion near the non-friction surface and the lowest at the portion nearthe friction surface.

The distribution of the amount of the resin of the friction material maybe made about 1% or more lower at the side of the friction surface thanan average rate of the resin in the friction material.

In this case, the resin amount becomes lower at the portion near thefriction surface than at the inside of the friction surface or at theportion near the non-friction surface.

The distribution of the amount of the resin may change two-dimensionallyin a width direction and the thickness direction of the frictionmaterial when the friction material is cut along a largest length.

In this case, the friction material can obtain a mechanical strengthcorresponding to a load direction, thereby having stable strength.

The two-dimensional change in the distribution of the amount of theresin may be such that the distribution of the amount of the resin ismade higher at an outer peripheral portion than at a central portion ofthe friction material.

In this case, the friction material can obtain a mechanical strengthcorresponding to a couple direction in which a load becomes large,thereby having stable strength.

According to a second aspect of the invention, there is provided amanufacturing method of a friction material comprising the steps of:making a resin contained in the friction material; and drying thefriction material. The drying step includes a step for making low atemperature at one surface of the friction material and/or making high atemperature at another surface of the friction material.

Therefore, the resin in the friction material has such a characteristicas to move from a low temperature part to a high temperature part whileled by a solvent that moves toward the high temperature part so as to bedried. Consequently, the resin amount distribution in the thicknessdirection becomes the lowest at the portion near the one surface. Thus,the friction material becomes ultrahigh heat resistant. Moreover, themanufacturing method forms a preferable resin amount distribution in thedrying step that the conventional art adopts except a characteristicfeature of the invention. Consequently, it is unnecessary to add steps,so that it can be practiced at low costs.

The drying step may further include a step for rotating the frictionmaterial in drying at a predetermined temperature condition so as tomake a distribution of an amount of the resin higher at an outerperipheral portion of the friction material by a centrifugal force inrotating.

In this case, the friction material can obtain a mechanical strengthcorresponding to a couple direction in which a load becomes large,thereby having stable strength.

According to a third aspect of the invention, there is provided amanufacturing method of a friction material comprising the steps of:making a resin contained in the friction material; and drying thefriction material. The drying step may include steps for drying twofriction materials with friction surfaces thereof overlapped with eachother and then hardening the friction materials at a high temperaturewhile separating the friction materials or keeping the frictionmaterials overlapped.

Therefore, a solvent does not dry from the friction surfaces that arefaced with each other. Rather, the solvent dries from the non-frictionsurface that is located outside. Then, the resin in the frictionmaterial moves while dragged by the solvent. Thus, a resin amountdistribution in a thickness direction becomes the highest at a portionnear the non-friction surface and the lowest at the portion near thefriction surface. Consequently, the friction material becomes ultrahighheat resistant. Moreover, the manufacturing method forms a preferableresin amount distribution in the drying step that the conventional artadopts except a characteristic feature of the invention. Consequently,it is unnecessary to add steps, so that it can be practiced at lowcosts.

The drying step may further include a step for rotating the frictionmaterial in drying at a predetermined temperature condition so as tomake a distribution of an amount of the resin higher at an outerperipheral portion of the friction material by a centrifugal force inrotating.

According to a fourth aspect of the invention, there is provided amanufacturing method of a friction material comprising the steps of:making two or more friction materials containing a different amount of aresin; and overlapping the friction materials so as to join the frictionmaterials into one body before finishing drying of at least one of thefriction materials containing the different amount of the resin.

Therefore, a plurality of friction materials that has a desired resinamount and that is dried appropriately are joined to make the resinamount distribution in the thickness direction the highest at theportion near the non-friction surface and the lowest at the portion nearthe friction surface. Thus, the friction material becomes ultrahigh heatresistant. For example, the friction materials are joined into one bodyduring the drying step in which they are dried to a certain orappropriate degree.

The drying step may further include a step for rotating the frictionmaterial in drying at a predetermined temperature condition so as tomake a distribution of an amount of the resin higher at an outerperipheral portion of the friction material by a centrifugal force inrotating.

According to a fifth aspect of the invention, there is provided amanufacturing method of a friction material comprising the steps of:impregnating a resin in a friction material; and drying the frictionmaterial. The impregnating step includes a step for impregnating resinshaving different viscosities in a front surface and a rear surface ofthe friction material, and the drying step includes a step for dryingthe friction material at a predetermined temperature condition whilelocating downward a side of the friction material at which the resinhaving a larger viscosity is contained.

Therefore, in case the predetermined temperature condition and theviscosity have a certain relation, namely, in case the temperature islow and the viscosity is high, a resin amount distribution in athickness direction from a friction surface side to a non-frictionsurface side of the friction material can be made lower at a portionnear the friction surface than at a portion having a highest resinamount in the thickness direction.

The drying step may further include a step for rotating the frictionmaterial in drying at the predetermined temperature condition so as tomake a distribution of an amount of the resin higher at an outerperipheral portion of the friction material by a centrifugal force inrotating.

According to a sixth aspect of the invention, there is provided amanufacturing method of a friction material comprising the steps of:impregnating a resin in a friction material; and drying the frictionmaterial. The impregnating step includes a step for impregnating anadditional resin on one surface of the friction material, and the dryingstep includes a step for drying the friction material at a predeterminedtemperature condition while locating outside a side of the frictionmaterial in which the additional resin is impregnated and giving acentrifugal force to the friction material in a thickness of thefriction material.

Therefore, a resin amount distribution in a thickness direction from afriction surface side, in which the additional resin is impregnated, toa non-friction surface side of the friction material can be made lowerat a portion near the friction surface than at a portion having ahighest resin amount in the thickness direction.

The drying step may further include a step for rotating the frictionmaterial in drying at the predetermined temperature condition so as tomake a distribution of an amount of the resin higher at an outerperipheral portion of the friction material by a centrifugal force inrotating.

Further objects and advantages of the invention will be apparent fromthe following description, reference being had to the accompanyingdrawings, wherein preferred embodiments of the invention are clearlyshown.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a graph showing a distribution of a resin amount in athickness direction of a lining portion of a friction material unitaccording to an embodiment and its modifications of the invention.

FIG. 2 is a graph comparing a heat spot resistance of the frictionmaterial according to the embodiment of the invention and that of aconventional material.

FIG. 3 is a graph comparing a μ-V positive inclination characteristic ofthe friction material of the embodiment and that of the conventionalmaterial.

FIG. 4 is a graph comparing an initial property of the friction materialof the embodiment and that of the conventional material.

FIG. 5 is an explanatory drawing showing a specific example of themanufacturing method of the friction material according to theembodiment of the invention.

FIG. 6 is an explanatory drawing showing another specific example of themanufacturing method of the friction material according to theembodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

One embodiment of the invention is described hereunder referring to FIG.1 to FIG. 4.

FIG. 1 is a graph showing a distribution of a resin amount in athickness direction of a lining portion of a friction material unitaccording to an embodiment and its modifications of the invention. FIG.2 is a graph comparing a heat spot resistance of the friction materialaccording to the embodiment of the invention and that of a conventionalmaterial. FIG. 3 is a graph comparing a μ-V positive inclinationcharacteristic of the friction material of the embodiment and that ofthe conventional material. FIG. 4 is a graph comparing an initialproperty of the friction material of the embodiment and that of theconventional material.

A friction material as a raw material of a friction material unitaccording to the present embodiment is a resin impregnated frictionmaterial. The present embodiment of the friction material can bemanufactured by a variety of manufacturing methods.

For example, a first manufacturing method of the present embodiment ofthe friction material has a drying step of the friction material. In thedrying step, a temperature at a friction surface of the frictionmaterial is kept low, while a temperature of an opposite surface(non-friction surface) being kept high. A resin in the friction materialhas a characteristic or tends to move from a low temperature portion toa high temperature portion by trailing behind a solvent that moves tothe high temperature portion so as to be dried. Therefore, adistribution of a resin amount in a thickness direction is the highestat a portion near the non-friction surface while being the lowest at aportion near the friction surface.

According to a second manufacturing method of the present embodiment ofthe friction material, friction surfaces of two friction materials arefaced and overlapped with each other and naturally dried thereafter fortwenty-four hours or more as they are. Then, the dried two pieces of thefriction materials are cured or hardened at a high temperature whilebeing separated from each other or being kept overlapped as they are. Inthis case, the solvent does not dry from the faced friction surfaces ofthe two friction materials but dries from the non-friction surfaces thatare disposed outside. Consequently, the distribution of the resin amountin the thickness direction is the highest at the portion near thenon-friction surface while being the lowest at the portion near thefriction surface, as in the first manufacturing method.

FIG. 1 show respectively the distribution of the resin amount in thethickness direction in the friction materials “Aa” and “Ab” made by thefirst and the second manufacturing methods. As shown in FIG. 1, in thefriction materials “Aa” and “Ab”, the distribution of the resin amountin the thickness direction is the highest at the portion near thenon-friction surface. The distribution of the resin amount decreases asit goes towards inside. Then, the distribution of the resin amount isthe lowest at the portion near the friction surface. The frictionmaterial having such distribution of the resin amount has an excellentproperty as the friction material starting with a heat spot resistancementioned below.

In a first modification “B” of a friction material of the presentembodiment, the distribution of the resin amount is not the lowest atthe portion near the friction surface. However, the distribution of theresin amount is lower at the portion near the friction surface than theother portion such as the portion near the non-friction surface. In asecond and a third modifications “C” and “D” of friction materials ofthe present embodiment, the distribution of the resin amount is lower atthe portion near the friction surface, though the distribution is not sosmooth as seen in the distribution in the embodiments “Aa” and “Ab”. Inthose cases, the friction materials show excellent heat spot resistance,too.

Next, a test for a heat spot resistance was carried out for a specificexample of a friction material according to the present embodiment ofthe invention and a conventional friction material as a comparisonexample. The specific example of the friction material was manufacturedas follows. First, two of the above described friction materialsaccording to the embodiment or modifications were overlapped on eachother while the friction surfaces are face with each other. Then, thetwo friction materials were naturally dried for twenty-four hours ormore while they are kept overlapped. Thereafter, the resin in thefriction materials was completely hardened at a temperature of 200° C.for one hour. Then, the friction materials were stuck to a core metal onwhich an adhesive was coated so as to obtain the friction material ofthe specific example. Thereafter, the heat spot resistance test wascarried out on the specific example of the friction material accordingto the present embodiment and the comparison example of the conventionalfriction material. The heat spot resistance test is a test in which afriction material is pressingly fitted to an iron material and rotatedwhile it is measured how many times the friction material rotates untila scorch (heat spot) is generated first on a surface of the ironmaterial. Thus, the heat resistance of the friction material isevaluated.

As a test machine, SAE#2 tester was used. The evaluation was carried outunder a condition of a rotating speed of 7800 rpm, an inertia amount of0.086 kg·m2, a face pressure of 785 kPa and an oil amount of 180 ml/min.A test result is shown in FIG. 2. It is seen that the heat spotresistance of the present embodiment of the friction material improvesup to almost fifteen times as large as that of the conventional frictionmaterial.

Next, a μ-V positive inclination characteristic was tested on thepresent embodiment of the friction material while compared with theconventional friction material. A test result is shown in FIG. 3. No μ-Vpositive inclination characteristic was confirmed on the conventionalfriction material. On the other hand, an outstanding μ-V positiveinclination characteristic is confirmed on the present embodiment of thefriction material. Thus, since the resin amount at the portion near thefriction surface is low in the friction material according to thepresent embodiment, an actual driving feeling improves such as a clutchproperty or a μ-V positive inclination characteristic.

Next, an initial property was tested on the present embodiment of thefriction material while compared with the conventional frictionmaterial. A test result is shown in FIG. 4. It is well seen that thepresent embodiment of the friction material improves in the initialproperty far better than the conventional friction material. Thus, sincethe resin amount at the portion near the friction surface is low in thefriction material according to the present embodiment, the initialproperty improves. Therefore, it is possible to stabilize a performanceof an AT (automatic transmission) from an initial stage.

As described above, in the present embodiment of the friction material,the distribution of the resin amount in the thickness direction at alining portion is lower at the portion near the friction surface than ata portion that has a highest distribution of a resin amount. Forexample, in the resin impregnated friction material, the drying iscarried out so as to make low the temperature at the friction surface ofthe friction material and make high the temperature at the non-frictionsurface. Thus, the distribution of the resin amount in the thicknessdirection of the lining portion of the friction material unit becomeslower at the portion near the friction surface than at the portion thathas the highest distribution of the resin amount. That is, the resinamount at the portion near the friction surface is lower than the insideof the friction material or the portion near the non-friction surface.Consequently, the heat resistance and the heat spot resistance improvesvery much. Thus, the present embodiment of the friction material becomesultra-high heat resistant.

Moreover, the distribution of the resin amount in the thicknessdirection of the friction material is determined by the drying step ofthe friction material. Then, it is unnecessary to carry out apost-treatment process. Consequently, it is possible to provide afriction material of ultra-high heat resistance at low costs without anydeterioration of the strength. Furthermore, since the resin amount nearthe friction surface is less, the clutch property, the μ-V positiveinclination characteristic and the actual driving feeling improve. Inaddition, since the resin amount near the friction surface is less, theinitial property improves. Therefore, the performance of the AT is madestable from the initial stage.

The “portion near the friction surface” means a portion or a range thathas a depth of about 10% from the friction surface in relation to theoverall thickness of the friction material. Moreover, a “resin rate” isdefined to mean a “resin amount per a unit volume”. Thus, it can bedefined that, in the present embodiment of the friction material, anaverage resin rate within the range having a depth of about 10% from thefriction surface in relation to the overall thickness of the frictionmaterial is lower than an average resin rate of the entire frictionmaterial. The same results are obtained if it is defined that an averageresin rate within a range having a depth of about 5% from the frictionsurface in relation to the overall thickness of the friction material islower than the average resin rate of the entire friction material.According to experiments of the inventors of the present application, itwas confirmed that an average resin rate within a range having a depthof about 40% from the friction surface in relation to the overallthickness of the friction material is lower than the average resin rateof the entire friction material. However, as judged from a propertyshown in FIG. 1, it is estimated that an average resin rate within arange having a depth a little larger than about 40% from the frictionsurface in relation to the overall thickness of the friction material islower than the average resin rate of the entire friction material.

In the present embodiment of the friction material unit, the frictionmaterials shown by “Aa”, “Ab”, “C” and “D” of FIG. 1 have the lowestresin amount distribution in the thickness direction at the portionsnear the friction surfaces, respectively. The above-mentioned effectsare obtained if the resin amount distribution in the thickness directionof the lining portion of the friction material is such that there existat the portion near the friction surface a portion having a high resinamount and a portion having a low resin amount or portions having resinrate of about plus 3% or more or minus 3% or less in relation to theaverage resin rate. Particularly, the above-mentioned effects areobtained if the resin amount distribution in the thickness direction ofthe lining portion of the friction material is such that there exist atthe portion near the friction surface a portion having a low resinamount or a resin rate less than about minus 3% in relation to theaverage resin rate.

Moreover, according to test results of the inventors, the presentembodiment of the friction material can be specified as a frictionmaterial that has an average resin rate of 0% to 50% at the portion nearthe friction surface and that has a lower average resin rate than theaverage resin rate of the entire friction material. In this case, it isthough that the same advantageous effects are also obtained.

Particularly, if the resin amount distribution in the thicknessdirection of the lining portion of the friction material is the lowestat the portion near the friction surface, the friction material can havean extremely high heat resistance and hear spot resistance so as to beultrahigh heat resistant. Moreover, the resin amount distribution in thethickness direction of the friction material is determined by the dryingstep of the friction material. Therefore, no post-treatment process isnecessary. Consequently, the friction material can be manufactured atlow costs and no deterioration of strength is caused thereto.Furthermore, even if a compounding rate or mixing amount of the resin ofthe friction material is increased in order to heighten the strength,the resin amount near the friction surface becomes less than theconvention one. Consequently, it is possible to heighten the strengthwithout affecting the heat resistance.

The manufacturing method of the friction material according to thepresent embodiment includes a step for keeping low the temperature atthe friction surface while keeping high the temperature at thenon-friction surface in the drying step of the friction material.Therefore, the resin in the friction material has such a property asmoving from the low temperature part to the high temperature part whilebeing led by the solvent that moves to the high temperature part andthat is dried thereafter. Consequently, the resin amount distribution inthe thickness direction becomes the lowest at the portion near thefriction surface. Accordingly, the friction material can be ultrahighheat resistant while having the above-mentioned excellentcharacteristics. Moreover, the present embodiment of the manufacturingmethod forms a preferable resin amount distribution in the drying stepthat is seen in the conventional art. Thus, it is unnecessary to addspecial steps, so that the present embodiment of the manufacture methodcan be practiced at low costs.

Particularly, the present embodiment has the step of drying naturally orat a room temperature the two friction materials that are overlapped oneach other while faced at their friction surfaces (First Method). Theproperty tests were carried out on the friction materials manufacturedby such step. However, the property is improved similarly also in caseof the friction material that is manufactured by decreasing the resinamount near the friction surface by making low the temperature at thefriction surface while making high the temperature at the non-frictionsurface in the drying step of the friction material (Second Method).

The method for decreasing the resin amount near the friction surface isnot limited to the above two methods. A variety of other methods can beadopted such as a depressurization, a pressurization, a centrifugalseparation, a one-side coating by a spray coating, a lip coating and aroller coating or the like, etc. Moreover, while the present embodimenthas been described on the resin impregnated friction material, thefriction material of the invention is not limited to the resinimpregnated one. The invention can be embodied into any type of frictionmaterials as long as it contains a resin as a component starting with aresin layered type.

Particularly, in case of using a powder resin, the inventive frictionmaterial can be similarly manufactured also by a step for mixing andkneading the powder resin so as to be evenly distributed when formingthe friction material and making low the temperature at the frictionsurface while making high the temperature at the non-friction surface inthe drying step of the friction material. Moreover, in the drying stepof the friction material having such even distribution, the power resinmay be spread or dispersed on one face of the friction material.Alternatively, the powder resin may be stuck to the one face of thefriction material so as to be impregnated therein.

The invention is not limited to the above embodiment with respect to theother structure, shape, number, material, dimension, relative connectionor the like. The invention is not limited to the above embodiment withrespect to the manufacturing method of the friction material or theother steps.

Normally, the manufacturing method according to the above embodiment ofthe friction material includes the step of making low the temperature atthe one surface and/or making high the temperature at the other surfacein the drying step of the friction material. Then, the resin in thefriction material has a characteristic such that it moves from the lowtemperature part to the high temperature part by being led or dragged bythe solvent that moves toward the high temperature part to be dried.Consequently, the resin amount distribution in the thickness directionbecomes the lowest at the portion near the one surface. Accordingly, thefriction material becomes ultrahigh heat resistant while having theabove described excellent characteristics. Moreover, the presentembodiment of the manufacturing method forms the preferable resin amountdistribution in the conventional drying step. Therefore, additionalsteps are unnecessary and it can be practiced at low costs.

The above embodiment of the manufacturing method of the frictionmaterial includes the step for drying the two friction materialsoverlapped with the friction surfaces faced with each other andthereafter hardening the friction materials while separating them orkeeping them overlapped. In this case, the solvent does not dry from thefaced friction surfaces but dries from the non-friction surface disposedoutside. Therefore, the resin in the friction material moves while beingled by the solvent so that the resin amount distribution in thethickness direction becomes the highest at the portion near thenon-friction surface and the lowest at the portion near the frictionsurface. Accordingly, the friction material becomes the ultrahigh heatresistant and has the above excellent characteristics. Moreover, thepresent embodiment of the manufacturing method forms the preferableresin amount distribution in the conventional drying step. Therefore,additional steps are unnecessary and it can be practiced at low costs.

The above-mentioned manufacturing method of the friction material makestwo or more friction materials having different resin amounts overlappedand joined as one body. Specifically, two or more friction materialshaving different resin amounts are formed first. Then, the frictionmaterials are overlapped on each other in an appropriately dried statebefore finishing drying while using at least one or more frictionmaterials having a different resin amount. Then, the friction materialsare stuck to each other via a binder so as to make one body. Thus, theresin amount distribution in the thickness direction becomes the highestat the portion near the non-friction material and the lowest at theportion near the friction material. Consequently, the friction materialbecomes ultrahigh heat resistant. That is, a friction material can bedried while making the resin amount less at the portion near thefriction surface and mounted on another friction material before dryingso as to be integrally joined. As a result, the resin amountdistribution in the thickness direction from the friction surface sideto the non-friction surface side of the friction material becomes lowerat the portion near the friction surface than at the portion having thehighest resin amount in the thickness direction. Moreover, it ispossible that plural friction materials be overlapped and the resinimpregnated therein so as to form a friction material having anon-continuous distribution between the faces of plural frictionmaterials.

As described above, the friction material according to the invention hasthe resin material distribution in the thickness direction of the liningportion, namely, in the thickness direction from the friction surfaceside to the non-friction surface side. The distribution is lower at theportion near the friction surface than at the portion having the highestresin amount in the thickness direction. In embodying the invention, thefriction surface and the non-friction surface or the front and the rearsurfaces of the friction materials that are dried appropriately in thedrying step are joined by the binder. Thus, it is possible to make theresin amount distribution in the thickness direction from the frictionsurface side to the non-friction surface side of the friction materiallower at the portion near the friction surface than at the portionhaving the highest resin amount. In this case, no post-treatment processis necessary. Consequently, the friction material of ultrahigh heatresistance can be obtained at low costs without deterioration of thestrength.

As described above, the resin amount distribution in the thicknessdirection from the friction surface side to the non-friction surfaceside of the friction material is made lower at the portion near thefriction surface than at the portion having the highest resin amount.Consequently, the friction material improves its heat resistance andheat spot resistance so as to be ultrahigh heat resistant. Moreover, theresin amount distribution in the thickness direction is determined inthe drying step of the friction material. Accordingly, no post-treatmentprocess is necessary. Consequently, the friction material can beultrahigh heat resistant at low costs without deterioration of strength.

The resin of the above embodiment of the friction material is 20% ormore lower at the friction surface side than at the non-friction surfaceside in the embodiment of the “Aa” of FIG. 1. Therefore, the resinamount near the friction surface becomes lower than that near thenon-friction surface. Thus, the heat resistance and the heat spotresistance improve very much, so that the friction material becomesultrahigh heat resistant. However, according to the experiments of theinventors, even if the resin amount is 5% or more lower at the frictionsurface side than at the non-friction surface side, it was confirmedthat the heat resistance and the heat spot resistance improved and thatthe property as the ultrahigh heat resistant friction material improved.As a result, it was revealed that it was enough if the resin amountdistribution in the thickness direction from the friction surface sideto the non-friction surface side of the friction material was made lowerat the portion near the friction surface than at the portion having thehighest resin amount in the thickness direction.

Particularly, in the above embodiment of the friction material, theresin amount is made about 5% or more lower at the friction surface sidethan at the inside of the friction material. Since the resin amount islower at the portion near the friction surface than at the inside of thefriction material. Consequently, the friction material is improved verymuch in the heat resistance and the heat spot resistance in the samemanner as the embodiment in which the resin amount is lower at theportion near the friction surface than at the portion near thenon-friction surface. As a result, the friction material becomesultrahigh heat resistant. Moreover, the resin amount distribution in thethickness direction is determined in the drying step of the frictionmaterial. Accordingly, no post-treatment process is necessary.Consequently, the friction material can be ultrahigh heat resistant atlow costs without deterioration of strength.

In the above embodiment, as shown in FIG. 1, the resin amountdistribution in the friction material is continuously changed.Therefore, it is prevented that a mechanical stress is applied to aspecific portion.

Moreover, in the above embodiment, as shown in FIG. 1, the frictionmaterial that changes the resin amount distribution continuously can bemanufactured as follows. That is, two or three or more frictionmaterials having different resin amounts are formed first. Then, thefriction materials are overlapped on each other in an appropriatelydried state before finishing drying while using at least one or morefriction materials having a different resin amount. Then, the frictionmaterials having the different resin amounts are stuck to each other viaa binder so as to make one body.

In this case, the friction material changes the resin amountdistribution in a discontinuous manner. However, it is possible to set aresin content rate as desired in the plural friction materials havingthe different resin amounts. Consequently, the friction material isimproved very much in the heat resistance and the heat spot resistanceand becomes ultrahigh heat resistant. Moreover, the resin amountdistribution in the thickness direction can be determined by theoverlapping. As a result, it is possible to obtain the ultrahigh heatresistant friction material at desired low costs.

The above embodiment of the friction material is formed by impregnationof the resin. That is, the temperature at the friction surface of thefriction material is decreased while the temperature at the non-frictionsurface being increased after the resin is impregnated therein. Then,the resin in the friction material has such a property as to move fromthe low temperature portion to the high temperature portion while beingled by the solvent that moves toward the high temperature portion andthat is dried thereafter. Consequently, the resin amount distribution inthe thickness direction becomes the highest at the portion near thenon-friction surface and the lowest at the portion near the frictionsurface. Therefore, the friction material can be easily manufactured atlow costs.

According to the experiments of the inventors, with respect to the resinamount distribution in the thickness direction of the above embodimentof the friction material, if the resin amount is about 1% lower at theportion near the friction surface than the average resin rate, the resinamount becomes lower at the portion near the friction surface than theinside of the friction material or the portion near the non-frictionsurface. Thus, the friction material is very much improved in the heatresistance and the heat spot resistance so as to be ultrahigh heatresistant. Moreover, the friction material can be ultrahigh heatresistant at low costs without any deterioration of strength.

The present embodiment of the manufacturing method of the frictionmaterial can be practiced such that it includes the step for making lowthe temperature of the one surface and/or making high the temperature ofthe other surface in the drying step of the friction material. The resinin the friction material has such a characteristic as to move from thelow temperature part to the high temperature part while dragged by thesolvent moving toward the high temperature portion so as to be dried.Then, the resin amount distribution in the thickness direction becomesthe lowest at the portion near the one surface. Accordingly, thefriction material becomes ultrahigh heat resistance while having theabove excellent characteristics. Moreover, the present embodiment of themanufacturing method forms the preferable resin amount distribution inthe conventional drying step. Consequently, no additional steps arenecessary. As a result, it can be practiced at low costs.

The present embodiment of the manufacturing method of the frictionmaterial includes the steps for drying two friction materials or two ormore friction materials with the friction surfaces thereof overlappedwith each other and then hardening the friction materials at a hightemperature while separating them or keeping them overlapped. In thiscase, the solvent does not dry from the friction surface faced andconfronted to each other but dries from the non-friction surface that islocated outside. Therefore, the resin in the friction material moveswhile dragged by the solvent. Thus, the resin amount distribution in thethickness direction becomes the highest at the portion near thenon-friction surface and the lowest at the portion near the frictionsurface. Moreover, the present embodiment of the manufacturing methodforms the preferable resin amount distribution in the conventionaldrying step. Consequently, no additional steps are necessary. As aresult, it can be practiced at low costs.

The present embodiment of the manufacturing method of the frictionmaterial includes the steps for additionally impregnating the resin intoone surface of the friction material in the step of impregnating theresin in the friction material, disposing the side, to which the resinis additionally impregnated, of the friction materials toward outsideand drying the friction materials at a predetermined temperaturecondition while giving a centrifugal force in its thickness direction.Consequently, it is possible to make the resin amount distribution inthe thickness direction from the friction surface side to thenon-friction surface side at the side to which the resin is additionallyimpregnated lower at the portion near the friction surface than at theportion having the highest resin amount in the thickness direction.

FIG. 5 is an explanatory drawing showing a specific example of themanufacturing method of the friction material according to theembodiment of the invention.

In the present embodiment of the manufacturing method of the frictionmaterial, a friction material 10 is impregnated with a resin. Next, in adrying step of the friction material 10, the friction material 10 isdisposed on a support 51. Then, the support 51 is mounted on a rotationdrum 50 via an engagement means 52. Thereafter, the rotation drum 50 isrotated to give a centrifugal force to the friction material 10 in thethickness direction. At the same time, the friction material 10 is driedat a predetermined temperature condition. Therefore, the resin amountdistribution in the thickness direction from the friction surface sideto the non-friction surface side of the friction material 10 can be madelower as desired at the portion near the friction surface than at theportion having the highest resin amount in the thickness directiondepending on the temperature condition and the centrifugal force.Alternatively, the drying step of the friction material 10 may include astep for drying the friction material 10 at a predetermined temperaturecondition while making a side having a larger viscosity resin of thefriction material 10 disposed outside and giving a centrifugal forcethereto in the thickness direction. In this case, the resin amountdistribution in the thickness direction from the friction surface sideto the non-friction surface side of the friction material 10 can be madelower as desired at the portion near the friction surface than at theportion having the highest resin amount in the thickness directiondepending on the viscosity condition, the temperature condition and thecentrifugal force in the front and the rear sides of the frictionmaterial.

While the above embodiments are described on the premise that thefriction material is two-dimensionally processed, the three-dimensionalprocess is possible as shown in FIG. 5.

FIG. 6 is an explanatory drawing showing another specific example of themanufacturing method of the friction material according to theembodiment of the invention.

Specifically, the friction material 10 is disposed on a center of arotation bed 60 that rotates at a predetermined rotation speed at thetime of drying the friction material 10 at a predetermined temperaturecondition. Thus, the resin amount distribution at a peripheral portionof the friction material 10 becomes high by a centrifugal force thereof.Accordingly, in addition to the above-mentioned embodiments, the resinamount distribution becomes high at the peripheral portion of thefriction material 10. Consequently, it is possible to obtain amechanical strength in such a direction as to enlarge a couple of forcecorresponding to a load. As a result, the friction material has a stablestrength.

That is, when the friction material 10 is cut along a diameter that isthe largest length thereof, the resin amount distribution changestwo-dimensionally in a width direction and a thickness direction in itscross-section. For example, in the embodiment of FIG. 6, suchtwo-dimensional change in the resin amount distribution means that theresin amount distribution is made higher at the outer peripheral portionthan the central portion. Moreover, the resin amount distribution changecan be obtained as desired according to the thickness of the frictionmaterial 10, the centrifugal force, the temperature and the resinviscosity.

The preferred embodiments described herein are illustrative and notrestrictive, the scope of the invention being indicated in the appendedclaims and all variations which come within the meaning of the claimsare intended to be embraced therein.

1. A manufacturing method of a friction material comprising the stepsof: impregnating a resin in a friction material; and drying the frictionmaterial; wherein the drying step further includes a step for rotatingthe friction material in drying at a predetermined temperature conditionso as to make a distribution of an amount of the resin higher at anouter peripheral portion of the friction material by a centrifugal forcein rotating.